Selective production of voices in electrical musical instruments



A. F. KNOBLAUGH ET AL v SELECTIVE PRODUCTION OF VOICES IN Oct. 16, 1951 2,571,141

ELECTRICAL MUSICAL INSTRUMENTS 2 Sheets-Sheet 1 Filed April 22, 1948 INVENTOM- fZBVIA/Vfl f. Mason/aw 400 ATTORNEYS- A. F. KNOBLAUGH ET AL 2,571,141 SELECTIVE PRODUCTION OF voICEs IN ELECTRICAL MUSICAL INSTRUMENTS Fi ed April '22, 1948 2 Sheets-Sheet 2 w -il JOHN F v/o on/v.

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Patented Oct. 16, 1951 SELECTIVE PRODUQTION OF VOICES IN ELECTRICAL MUSICAL INSTRUMENTS Armand F. Knoblaugh, Cincinnati, and John F. Jordan, Terrace Park, Ohio, assignors to The Baldwin Gompany, Cincinnati, Ohio, a corporation of Ohio Application April 22, 1948, Serial No. 22,624

14 Claims. 1

This application is a continuation-in-part of our copending application of the same title, Serial No. 709,352, filed November 12, 1946, now abandoned.

Our invention relates to electrical musical instruments, and in particular to those in which tones of various qualities or voices are secured principally through filtering complex electric oscillations generated for tone production. Such instruments are in general simpler than those in which oscillations of simple wave form are generated and then combined synthetically to produce desired voices.

: The use of filter circuits upon oscillations of complex wave form will not, however, in itself give all of the voices which may be desired in an instrument of wide range. The original relationship of strengths of harmonics in a generated oscillation can be very substantially modified, but it is not possible by usual modifying circuits to eliminate entirely or substantially certain harmonics which are not desired for certain voices. For example, a number of orchestral wood wind instruments and certain organ pipes produce tones which have a large content of the odd order harmonics and an insignificant content of the even order-harmonics. Such voices cannot accurately be attained by filtering an oscillation which, as generated, corresponds to a rich or full tone containing both the even and the odd order harmonics in large amplitudes.

Winston E. Kock, in the United States Patents Nos. 2,148,478 and 2,233,948 taught the initial generation of complex oscillations which could be used with filter circuits for a number of voices requiring both even and odd order harmonics. For the attainment of voices requiring a suppression of the even order harmonics, he taught combining the oscillations of a given note with those of the note an octave above, one of the two being reversed in phase and adjusted as to strength. The result was that the harmonics of the higher note substantially cancelled the even order harmonics of'the lower note, thus giving a tone containing large amplitudes of the odd order harmonics with little or no amplitudes of the even order harmonics. The essentials of the Kock system involved the initial generation of oscillations which were rich in both even and odd order harmonics, the accurate maintenance of an exact phase relationship between octavely related tones as generated, and the provision of means for shifting or changing the phase of certain oscillations and controlling their strengths for combination.

An object of this invention is the provision of simpler and less expensive means for obtaining a wide variety of voices including tones rich in even order harmonics, tones rich in odd order harmonics and tones rich in both. Any or all of the oscillations so obtained can be modified by filter circuits.

It is also an object of our invention to provide a system in which the phase relationship of electric oscillations to be combined for the production of any given voice, becomes a matter of no moment.

It is a further object, in keeping with the other objects, to provide an instrument in which the tones throughout the musical scale compass are effectively balanced or desirably related in strength.

It is an object of our invention to provide a process and organization of apparatus in which the tones as generated are rich in the odd order harmonics and contain little or none of the even order harmonics, and in which octavely related tones of this type may be combined for voicing purposes in such a way that tones of higher frequency supply to the tone of lowest frequency useful amplitudes of some at least of the missing even order harmonics.

It is an object of our invention to provide a process and apparatus in which such tones may be so combined as to accomplish the end of producing the auditory effect of a single tone based upon the fundamental of the lowest frequency tone and containing both the even and odd order harmonics, rather than an auditory effect of octave coupling.

The more specific objects of the invention which will be pointed out hereinafter, or will be apparent to one skilled in the art upon reading these specifications, we accomplish in those procedures and through the use of those apparatus elements of which we shall now describe certain exemplary embodiments.

Reference is made to the accompanying drawings, wherein:

Figure 1 is a representation of one kind of a symmetrical wave form.

Figure 2 is a diagrammatic and fragmentary representation of apparatus elements which may be used in generating an electric oscillation having the wave form of Figure 1.

Figure 3 shows another type of symmetrical wave form.

Figure 4 is a diagrammatic and fragmentary view of apparatus elements with which an oscil- 3 lation of the wave form of Figure 3 may be generated.

Figure 5 shows yet another type of symmetrical wave form.

Figure 6 is a diagrammatic representation of the elements of an instrument involving our invention and showing one type of means whereby generated electric oscillations may be selectively combined.

Figure 7 is a diagrammatic representation of another instrument, again showing means whereby generated electric oscillations may be selectively combined.

Our system depends upon the initial generation of oscillations containing large amplitudes of the odd order harmonics, and low amplitudes or none at all of the even order harmonics. Thus at the outset, our generated oscillations are of the kind encompassing voices which for convenience we shall call wood wind voices, and which are suitable for use as such or with filtering for the obtaining of a variety of voices hitherto produceable in filter type instruments only by reversing the phase of and combining oscillations. In'using the term, oscillations, we include pulsations, i. e., cyclic variations in which there are unidirectional or direct current components.

For the production of voices requiring substantial contents of the even order harmonics, we combine octavely related oscillations as generated, the result being the addition of the even order harmonics as will be shown below. Other combinations are also possible, as we shall set forth.

To illustrate the manner in which our combinations operate, we show below at O, a partial qualitative analysis of an oscillation as generated by us. It will be noted that it contains a first harmonic (fundamental) of a frequency f cycles per second, and odd order harmonics comprising a third harmonic of a frequency 3 (3X)) a fifth harmonic 5f, etc. Also shown below, at 2-O, is an analysis of the oscillation for a note an octave above that corresponding to O and containing a first harmonic of a frequency 2 a third harmonic 6f, a fifth harmonic 10f, etc. Further shown, at 4-0, is an analysisof the oscillation two octaves above 0 and containing a first harmonic of a frequency 4 a third harmonic 12 etc.

Now it will be seen in the above analysis that the first harmonic of the oscillation 2-0 corresponds to the missing or zero value second harmonic of oscillation O, the third harmonic corresponds to the missing sixth harmonic, and the fifth harmonic to the missing tenth, etc. Thus by combining these two oscillations we obtain harmonics related to the lowest fundamental as certain ones of the even order harmonics, the odd order harmonics remaining as generated in the oscillation O. The combination of O and 2-0 may be further modified by adding 4-0 to supply oscillations corresponding to others of the even order harmonics, namely the fourth, twelfth, etc. harmonics.

In the practice of our invention, we generate initially complex oscillations of substantially symmetrical wave form. By this we mean a wave form in which each half cycle is substantially a mirror image of the preceding one. This type of oscillation is characterized by the presence of the odd order harmonics, but very little if any (if of of the even order harmonics. There are a Wide 4 variety of wave forms in this classification. A pure sine wave is of course a symmetrical wave form; but it is not a complex wave form because the amplitudes of the odd order harmonics in it, except for the first harmonic (fundamental) are zero. As a sine wave is departed from and symmetry is substantially retained, the amplitudes of various odd order harmonics increase, while the even order harmonics either do not appear or remain very low in amplitude.

In Figure 1, we have shown at l a fiat top wave form with sloping sides, which is a symmetrical wave form, as can be seen in dotted lines, by

moving one of the half cycles over to a position underneath the preceding half cycle. This flat top wave form, or the rectangular wave form (also a symmetrical wave) which it approaches, i one which can be generated in a number of ways. It can, for example, be generated by moving electrical contact members, carefully controlled as to time, or by commutators, or the like. Itcan also be generated photoelectrically as by providing a rotating member with a series of opaque and transparent portions of equal length and constant width, and scanning these by means of a stationary member containing a narrow slit. By way of explanation the sloping sides of the wave form of Figure 1, when generated photoelectrically, are due to practical lower limits of the Width of the slit, the narrower the slit the steeper the sides. Theoretically, a slit of zero width would produce a wave form with vertical sides,

, i. e., a rectangular Wave form.

In Figure 2 we have diagrammatically indicated a rotating disc 2 bearing a frequency track stood that such a device will be employed with a source of light on one side and a photocell on the other. The transparent areas 3 have been shown as substantially rectangular in configuration,,and spaced the Width of one such area.

Other wave forms than the flat top form of Figure 1 can be generated by making the transparent areas 3 of other shapes, and such other wave forms may also be symmetrical. Thus we are by no means confined to the relatively geometrically simple wave forms illustrated here- 111.

In Figure 3 we have shown another type of symmetrical wave at 6, a triangular wave form which may also be generated photoelectrically as shown in Figure 4, using the same type of disc 2 and transparent areas 3 in a sound track, but employing an opening 1 in the member 4, which opening is of the same width as the transparent areas 3.

It will be understood that the disc 2 may bear a large number of sound tracks for different notes, in which tracks the light openings 3 are arranged to produce the desired frequencies when the disc rotates at a selected speed.

The light openings in the sound tracks will preferably be arranged in accordance with a series of whole numbers related to each otherso nearly in accordance with the several frequencies in the equitempered musical scale as to give the desired musical eifect.

Again, complex oscillations having symmetrical wave forms, or Waveforms sufficiently symmetrical for our purpose, may be generated by purely electrical means employing thermionic tubes or gaseous discharge tubes. By way of example the curve 8 in Figure 5 is a curve characteristic of an appropriate charging and discharging of a con;

denser .of suitable size, which operation may be controlled by thermionic or gaseous discharge means: and it will be noted that the curve is very nearly symmetrical. In this way also, the effects contemplated in our invention may be :obtained. Means of the kinds referred to for generating symmetrical wave forms are not themselves novel, but are known in the art and are-not herein claimed as such.

Thus we are notlimited to the use of any particular type of oscillation generating means, the desideratumLbeing the production of complex oscillations characterized by symmetrical wave forms, i. e., containing substantial amplitudes of -.the odd1order harmonics and relatively very minor amplitudes, or none at all, of the even order harmonics. As we have already indicated, our oscillations as generated, and with or without filtering, are useful for the production of so- :called wood wind voices. In the practice of our invention we combine such oscillations with similar, harmonically related oscillations, in such a way as to gain the effect of full tones, i. e., oscillations characterized by wave forms containing substantial amplitudes of both the even order and the odd .order harmonics, which are useful with or without filtering for the production of the remaining voices of the instrument. This is accomplished by a method and means hereinaiter described.

vIn ourmethod of combination there is no question of mutual reinforcement or cancellation. {I'he combining of octavely related oscillations of the type we employ is to supply to a, lower frequency oscillation containing essentially odd prder harmonics one or more oscillations whose harmonics (likewise odd order as generated) correspond only to missing even order harmonics of the first oscillationas was shown above at 0, 2 0, -.4-O. There is thus no question of adding or subtracting strengths of harmonic components of coincident frequency, and thus no need to take account of phase relationships between oscillations. The method is an additive method.

In an instrument built in accordance with our method the only place where an eiTect of cancellation could occur would be from keyboard to keyboard, i. e., where the same tones are being simultaneously played on more than one keyboard. There an effect of cancellation could be obtained as between oscillations of substantially the same amplitude, providing these oscillations happened to be substantially exactly out of phase with each other.

of instruments by deriving the tones of all keyboards from a single set of generators. In other types of instrument, where it may be necessary or convenient to derive the tones for difierent keyboards from different sets of elements, care must be taken to generate oscillations for tones of similar pitch always in an in-phase relation ship. For example, in a photoelectric type of instrument, in-phase placement of slit assemblies will accomplish the purpose, as will the in-phase operation of contact members, pick-ups on tone wheels, and the like, in other types of instrument.

The combination of generated oscillations will, for an instrument of a Wide variety of voices, be selective. In the terminology of the pipe organ wherein playing keys may each sound tones of several pitches individually or in octave or other harmonious combinations, it is customary to speak of certain tones as 8 foot tones, those respectively an octave above sounded by the same keys as v4 foot tones, those an octave below as 16 foot tones, etc. It will now be understood that in our instruments, .by multiple shutters or key switches, we may derive electric oscillations for 8 foot tones in one header of electrical circuit, those for 4 foot tones in another header or electrical circuit, and so on, when any given playing key is depressed. These circuits can be made to feed filter or voice circuits individually or in combination,selectively, by appropriate switches in connection with organ stop tabs or the like. -We have not herein set forth filter circuits in detail; but reference may be made to those disclosed in the aforementioned Kock Patent No. 2,233,948. Similar filter .circuits, with or without modification may be employed in our system to give as wide a range of voices as is desired.

In a photoelectric type of instrument, it is our practice to derive electric oscillations for 8 foot .tones from a single photocell, the circuit of which constitutes the 8 foot header. Simultaneously acting shutters and another photocell are employed for deriving 4 foot pulsations in a 4 foot header, and so on. Again, the question of phase as between the .8 foot, the 4 foot, and other head- .ers is of no importance, for any given keyboard. Above, we have indicated how, for desired "full" tone voices, oscillations in ,4 foot headers may be added to those in the 8 foot header. Additionally, enrichment in the same direction may be obtained by adding oscillations in a 2 foot header. For certain effects it may be desired to add oscillations from a 16 foot header. Oscillations corresponding to harmonically related tones other than octavely related tones, may also be added. Desirable special voices may be obtained in this way; and in the practice of our invention we are not limited to the simple addition of 8 foot and 4 foot oscillations, as will be evident.

In Figure 6 we have shown diagrammatically 1 1. 8 elements of a photoelectric instrument with which our invention may be practiced. A pitch disc ll bearing pitch tracks (octavely related ones being indicated at is and I9), is mounted on a shaft 20, and is rotated by any suitable means. We have shown apertured plates 2| and 22, each of which will have a series of apertures, such for example as illustrated at Tin Figure 4, there being an appropriate aperture for each of the pitch tracks on the disc. A shutter mechanism will be provided for each plate. We prefer to employ shutter mechanism such as that described in the co-pending application of Edward M. Jones, entitled Photoelectric Music Instruments, Ser. No. 688,577, filed August 5, 1946, which issued on July 5, 1949, as U. S. Patent No. 2,474,847. The shutter movement therein set forth, wherein the shutter moves transversely to the motion of the corresponding pitch track, obviates a change in harmonic content of the oscillations as the shutter opens and closes and also avoids changes in frequency in the oscillations during the shutter motion. Shutter elements for the two indicated pitch tracks plary playing key 21, electrical pulsa'tionswill be produced simultaneously in photocells 3| and 35, but of octavely related frequencies.

Each photocell is shown as connected toits own preamplifier 36 and 37. The, preamplifiers are in turn connected to a system of filter circuits controlled by stop tabs. Assuming that 8 foot oscillations are derived from preamplifier 31 and 4 foot oscillations from 36, we have shown the latter as connected to a resistive stop switch 38 controlled by a stop tab 39. The resistive switch is connected to a filter circuit 40 for the production of a 4 foot voice. The preamplifier 36 is also connected to aresistive switch 4| while the preamplifier 3Lis connected to a stop switch 42, both being controlled by a stop tab 43 and both being connected to a filter circuit 44 for the production of a combined voice. The preamplifier 3! is again shown as connected to a stop switch 45 operated by a stop tab 46 and connected to a filter circuit 41 for the production of. an 8 foot voice. i

The various filter circuits feed a header 48, connected to a main amplifier 49, delivering power to a loud speaker 50. It will be understood from this diagrammatic showing that the number of filter circuits may be increased as desired. Likewise, aperture plates and shutter assemblies together with photocell systems may be added to take care of the combining of additional oscillations and the provision of additional keyboards.

Figure 7 is a diagrammatic representation of the derivation of oscillations in various headers by switching means as distinguished from photoelectric means. For other types of generators, inclusive of thermionic and gaseous discharge circuits, it will be our practice, as shown in Figure 7, to connect harmonically related generators 9, 9a, 9b, etc., to switch groups Ill, liia, I'Cl'b, etc., arranged for simultaneous operation by individual playing keys. The switches are arranged to close individual circuits between the generators and headers ll, l2 and I3. Switches l4, I and i6 which constitute, or are part of stop tab switch systems, determine the feeding of oscillations from the several headers individually, or in selective combination, to one or more filter or voice circuits. 1

The mere addition of octavely related sym metrical wave form oscillations as hereinabove described is not suflicient to produce the desired efiect of tone enrichment. When such oscillations, generated or derived at substantially the same amplitude are combined, while some Derceptible tone enrichment may occur, the effect on the ear is unmistakably that of the octave coupling of wood-wind tones. While octave coupling is sometimes desirable, one of the objects of this invention is to provide an instrument in which, by the combination of octavely related os cillations lacking the even order harmonics, a single tone, based upon the lowest fundamental of the combined oscillations, may be produced, which will be a full or rounded tone by reason of the effective presence of the even order harmonics.

We have shown above how the odd order harmonics of higher frequency octavely related oscillations correspond to the even order harmonics of a lower frequencyoctavely related osci'lation. But to avoid the effect of coupling, and to gain the single effect of tone enrichment, it is necessary to control the amplitudes of the combined oscillations to different values, and in particular to decrease the amplitude of the'higher frequency oscillation or oscillations.

. The use of a rectangular wave form provides an oscillation in. which there are no even order harmonics, and in which the first harmonic (fundamental) has three times the amplitude of the third harmonic, five times the amplitude of cillations of this kind aregenerated in a musical instrument at approximately the same effective amplitudes, the addition of a higher frequency oscillation to a lower frequency oscillation will provide for the latter a second harmonic (the fundamental of the higher frequency oscillation) of an amplitude substantially equivalent to the amplitude of the fundamental of the lower frequency oscillation and hence departing radically from the normal series of harmonic amplitudes in a full or rounded tone based on the same lower frequency fundamental and containing the generated amplitudes of the odd order harmonics. This gives to the ear an unmistakable effect to octave coupling and defeats one of the purposes of this invention.

' The effect of octave coupling can be avoided by decreasing the amplitude of the higher frequency oscillation to a point where the amplitude of its fundamental responds more nearly to the amplitude of the missing second harmonic of the lower frequency oscillation. An exact mathematical relationship is not required; but a substantial lessening of amplitude is necessary. We

n have found that in combining substantially triabout two-thirds the amplitude of the next lower frequency octavely related oscillation. For other specific types of symmetrical wave forms the degree of attenuation required will depart some what from the value given but can easily be ascertained by combining octavely related oscillations and attenuating the higher one until the ear no longer hears the combined oscillations as octavely coupled woodwind tones.

The attenuation required in the light of this teaching is easily applied byinserting electrical attenuation means in the various headers individually, as at 5! and 52 in Figure '7, or by the derivation of oscillations from the various headers or circuits through branch circuits containing resistances of appropriate values. Thus in Figure 6 where 8-foot and l-foot oscillations are sent concurrently through the filter circuit 45, the resistance 53 in the circuit of the l-foot oscillations may be made sufficiently higher in value than the resistance 54 in the circuit of the 8-foot oscillations to produce the attenuation required.

In instruments employing filtering means, especially polyphonic instruments, the filtering may upset the tonal balance of a series of complex oscillations of different frequency. Hence there is the problem of attaining tonal balance so that a uniformity of tonal strength is effected throughout the musical-scale compass of the instrument. This is especially important in instruments employing the teachings of this invention, since if a single attenuating means in .a header or branch circuit for higher frequency oscillations is to be employed to reduce their amplitude with respect to the amplitude of lower frequency octavely related oscillations, this will not be accomplished throughout the range of the instrument unless tonal balanceis attained.

Means for tonal balance are taught in the aforementioned Kock Patent 2,233,948 with particular application to an instrument in which complex electric oscillations are generated, collected in headers, and filtered for various voices, the balancing means comprising attenuating resistances applied to the collecting headers between various points of connection from these headers to difierent ones of the generators throughout the frequency range of the instrument. In an instruments of the type diagrammatically illustrated in Figure '7, we may employ the balancing means of -s the Kock patent.

In photoelectric instruments balance can be obtained in various ways, as for example, by using larger shutter openings for notes which it is desired to strengthen (e. g. high-pitch notes which i tend to be reproduced with too little relative volume) or by making the transparent areas in the pitch tracks more or less resistant to the passage of light selectively, as between pitch tracks, or by using means in the nature of a gray scale or optiscribed or by the use of certain voice boxes of D branch circuits for the higher frequency oscillations containing controlling resistors substantially no greater in value than the corresponding resistors in the branch circuits of the lower frequency oscillations.

Modifications may be made in our invention without departing from the spirit of it. Having thus described our invention in certain exemplary embodiments, what we claim as new and desire to secure by Letters Patent is:

1. In an electrical musical instrument, generating means for generating, over the range of the instrument, complex electric oscillations of symmetrical wave form, said oscillations containing substantial amplitudes of odd-order harmonics and non-substantial amplitudes of even-order harmonics, and circuit means for simultaneously deriving in an output system octavely related ones of said oscillations, said circuit means comprising attenuating means for reducing the amplitude of the higher frequency oscillations as respects the amplitude of lower frequency octavely related oscillations.

2. In an electrical musical instrument, generating means for generating over the range of the instrument, complex electric oscillations of symmetrical wave form, said oscillations containing substantial amplitudes of odd-order harmonics and non-substantial amplitudes of even-order harmonics, circuit means for deriving harmonically related oscillations simultaneously from said generating means, and circuit means for combining the said harmonically related oscillations in relative, controlled amplitudes to produce a single tone containing substantial amplitudes of both evenand odd-order harmonics.

3. In an electrical musical instrument, generating means for generating over the range of the instrument complex electric oscillations of symmetrical wave form, said oscillations containing substantial amplitudes of odd-order harmonics and non-substantial amplitudes of even-order harmonics, playing keys, switch means in connection with said keys for feeding said oscillations to a header, switch means in connection with said playing keys for simultaneously feeding octavely related oscillations to another header, circuit means for combining the oscillations in said headers, including attenuating means in connection with the header for the higher frequency oscillations to reduce the amplitudes of said oscillations to a value substantially below the amplitudes of the oscillations in the other of said headers.

4. In an electrical musical instrument, generating means for generating over the range of the instrument complex electric oscillations of symmetrical wave form, said oscillations containing substantial amplitudes of odd-order harmonies and non-substantial amplitudes of evenorder harmonics, playing keys, switch. means in connection with said keys for feeding said oscillations to a header, switch means in connection with said playing keys for simultaneously feeding octavely related higher frequency oscillations to another header, a plurality of voice circuits containing filtering means, circuit means in connection with a voice circuit for feeding oscillations thereto from said first header, and circuit means in connection with another voice circuit for feeding oscillations thereto from both headers, said circuit means containing attenuating means for reducing the amplitudes of the oscillations in said second header to a value substantially below the amplitudes of the oscillations in said first header.

5. The structure claimed in claim 4 in which said headers contain attenuating means for balancing the tonal scale.

6. In an electrical musical instrument, generating means for generating over the range of the instrument complex electric oscillations of symmetrical wave form, said oscillations containing substantial amplitudes of odd-order harmonics and non-substantial amplitudes of even-order harmonics, playing keys, switch means in connection with said keys for feeding said oscillations to a header, switch means in connection with said playing keys for simultaneously feeding octavely related higher frequency oscillations to another header, a plurality of voice circuits, circuit means in connection with a voice circuit for feeding oscillations there to from said first header, circuit means in connection with another voice circuit for feeding oscillations thereto from both headers including means for differentially attenuating the higher frequency oscillations with respect to the lower frequency octavely related oscillations, circuit means in connection with another voice circuit 11 for feeding oscillations thereto from said second header, and filtering means in said Voice circuits.

7. In a photoelectric musical instrument, pitch disc means, means for producing from said pitch disc means and in the circuit of a photocell oscillations selected by the actuation of playing keys, said oscillations being of symmetrical Wave form, and containing substantial amplitudes of oddorder harmonics and non-substantial amplitudes of even-order harmonics, and means simultaneously actuable by the same playing keys for reproducing in the circuit of a second photocell harmonically related higher frequency oscillations derived from the same pitch discmeans, attenuating means for said higher frequency oscillations and means for obtaining voices from the derived tones including means connectible to the circuit of said first mentioned photocell and means connectible to the circuits of both photocells.

8. A process for the derivation of a variety of voices in an electrical musical instrument, said process comprising the step of generating complex electric oscillations initially containingsubstantial amplitudes of the odd-order harmonics and non-substantial amplitudes of the evenorder harmonics, deriving at least one voice from the oscillations so generated, and deriving at least another voice from said oscillations in combination with higher frequency harmonically related electric oscillations of similar charactcristics, controlled in amplitude to avoid the effect of octave coupling.

9. A process of providing voices in electrical musical instruments which process comprises the generation of complex electric oscillations which as produced, contain substantial amplitudes of the odd-order harmonics and. non-substantial amplitudes of the even-order harmonics, and as desired, adding even-order harmonics to the said oscillations by adding thereto substantially lesser amplitudes of octavely related electric oscillations of similar characteristics.

10. A process of deriving wood wind and full tones in an electrical musical instrument, which process comprises generating complex electric oscillations containing the fundamental and oddorder harmonics, but substantially devoid of even-order harmonics, employing such oscillations for producing wood wind voices, and adding even-order harmonics to said oscillations for full voices by combining with them substantially lesser amplitudes of harmonically related higher frequency electric oscillations, the odd-order harmonics of which respond to the even-order harmonics of the first mentioned oscillations.

11. A process of providing voices in electrical musical instruments, which process comprises the generation of complex electric oscillations which as produced have a substantially symmetrical wave-form, and as desired, adding evenorder harmonics to the said oscillations by adde ing thereto octavely related electric oscillations of similar characteristics, said octavely related oscillations being controlled as to amplitude with respect to said first mentioned oscillations to be not greater than substantially two-thirds the amplitude thereof.

12. A process of providing voices in an elec- 13. A process of providing voices in electrical musical instruments, which process comprises the generation of complex electric oscillations which as produced are characterized by a funda- 'mental frequency, and a descending series .of'

amplitudes of harmonicsas respects the amplitude of said fundamental frequency, said harmonics consisting of the odd-order harmonics, reproducing said oscillations as wood wind tones, and combining said oscillations with octavely related higher frequency electric oscillations of similar type while diminishing the amplitudes of said higher frequency oscillations so that the amplitudes of their fundamental frequencies correspond roughly to the amplitudes of the missing even-order harmonics in said series, whereby to produce full tones.

14. In a polyphonic electrical musical instrument for producing complex musical tones according to a multi-octave musical scale, each said tone being characterized by an integer series of evenand odd-order harmonic components of amplitudes decreasing inversely as the order of the harmonic, generating means producing polyphonically a series of complex oscillating electric potentials having odd-order harmonics but lacking suflicient amplitudes of even-order harmonics to produce said tones, playing keys, means associated with each said key for deriving from said generating means one of said series as needed to meet the requirements of a polyphonic musical composition, additional means associated with each said key for'concurrently deriving from said generating means a group of oscillating potentials having a higheroctave relationship to said needed potentials, a plurality of collecting means each providing a common path for electric potentials bearing the same octave relationship to remaining potentials in a concurrently, derived group, means in connection with said plurality for combining said needed potentials with said octavely related po-' tentials, said last-mentioned means including electrical impedance means for controlling the amplitudes of said octavely related potentials to supply the lacking amplitudes of even-order harmonics.

ARMAND F.-KNOBLAUGH. JOHN F. JORDAN.

' REFERENCES CITED The following references are of record in the file of this'patent:

V UNITED STATES PATENTS Number 

